The wings of an aircraft are subject to numerous forces during takeoff, flight, and landing. Aircraft use wing spars to evenly distribute those forces. Each wing will have multiple wing spars radiating out from the fuselage (on both the bottom and top side of the wing) toward the tip of the wing. The wing spars carry these forces to ensure that each part of the wing surface carries a proportionate share of the load.
Each wing spar has two fuselage ends (one on the top of the wing and one on the bottom of the wing) that can insert into paddle fittings attached to the fuselage. A paddle fitting has a fork-shaped receptacle end for receiving the end of a wing spar. One method of holding the wing spar stationary within the paddle fitting involves drilling a hole through both forks of the paddle fitting and the wing spar, inserting a fastener through the hole, and tightening the paddle fitting/wing spar assembly to a specified torque.
Due to the exact tolerances required in building aircraft, the drilled hole must be both the appropriate diameter and concentric through both forks of the paddle fitting and the wing spar. A hole that is drilled too large or is non-concentric will degrade too rapidly under the operational forces of an aircraft. A manually operated drill cannot drill a hole through this material stack up that will meet these exact tolerance requirements on a consistent basis. These precise tolerances necessitate a device, such as a paddle fitting tool, that clamps to the paddle fitting/wing spar assembly to hold the drill stationary as the drill bit drills the hole through the paddle fitting and the wing spar.
To ensure the drilled hole has the appropriate dimensions and concentricity, conventional paddle fitting tools use a guide or fixture coupled to the drill. One example of such a conventional paddle fitting tool is manufactured by Boeing under drawing number ST7220C-1 that describes a Quackenbush 15QDR-RAB-SU-RS drill attached to a fixture having an air pressure cylinder to clamp the paddle fitting tool to the paddle fitting in order to hold the paddle fitting, and consequently the wing spar inserted within the forks of the paddle fitting, stationary.
However, these conventional paddle fitting tools have several limitations, including safety, cost of manufacture, and speed of operation. The air pressure cylinders typically clamp relatively rapidly and can therefore injure an operator. Another potentially dangerous situation can arise if the paddle fitting tool disengages from the paddle fitting while the drill is still operating. This can occur if the air pressure cylinder malfunctions (for example, due to air line deterioration or the air pressure being cut off). This can also occur because the air pressure cylinders typically cannot achieve a clamp force of six hundred pounds per square inch (psi) or greater.
Conventional paddle fitting tools can also be relatively slow because of the difficulty in locating and clamping the tool at the correct position on the paddle fitting.